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Stellar astronomy
Nils Wiki>Natural Sciences>Physical Sciences>Astronomy>Stellar astronomy ---- Life of Stars The life of a star starts in molecular clouds containing 75%H, 24%He and 1% other trace elements. The interstellar cloud collapses, and starts to pull inwards. Certain places in the cloud, the collapse goes faster especially in the center. The temperature in center becomes so great that it turns into a (himmellegeme) At this stage before the fusion starts, the star is called a proto-star. At about 10 million K nuclear fusion stars by fusing hydrogen into helium. The gravitational pull inwards, and the photon pressure outwards balance each other. Most of the stars life is now on the main sequence, for about 10 billion years. When most of the hydrogen is burned up, the core gets pushed together. A shell of hydrogen around the core is still fusing, and the shell moves outwards in lack of more fuel, leaving the helium in the core. The outer layers of the sun grows very much, and we get a red giant. At 100 million K, helium fuses to carbon. The helium"Wave" (blaffet) is an explosion that make the temperature and size increase a lot. The core consist now of carbon, and a layer of helium is burning outwards, behind the hydrogen burning. If the stars mass is very big, the star will expand outwards to a super giant. The giant throws it's outer layers away in a violent explosion, and makes a planetary fog. Different outcomes when stars end their life Mass (Msun) Description Ending Product m < 0.08 The temperature does not get high enough that nuclear fusion starts in the core. The star ends it's life as a Proto-Star Brown Dwarf m < 8 The "Carbon Cyclus" ends so that the fusion energy disappear. The core collapses until the electron degeneration pressure balance the gravitational pull inwards. The temperature is high at first, then it slowly drops for a billion years, until the star is no longer shining. The maximum limit for white dwarfs are 1,4 Msun White Dwarf -> Black Dwarf Double Stars If the double stars have different mass will the stars life also be different. If on of the stars becomes a white dwarf while the other one is a red giant, will the strong gravitational pull from the white dwarf pull mass from the red giant. If the dwarfs mass exceed 1,4 Msun will it collapse. The fusion processes will go mental, and explodes in a supernovae type 1a. Supernovae Type 1a m > 8 At this big masses, the stars will not halt the fusion processes by carbon and oxygen, but starts to fuse into neon and magnesium. At the end iron is produced. When the iron core exceeds 1,4 Msun, there is nothing which can stop the gravitational pull inward, and even the electron degeneration pressure will not keep the core from collapsing. The collapse goes tremendously fast, and forces the electrons to combine with the protons. Proton + Electron = Neutron. The core of the star is now a big collection of neutrons. When the collapse finally halt, due to the ??-pressure, the star explodes, most likely due to the vast amount of neutrinos thrown outwards from the core. If there is still something left of the core after the supernovae, this will become a neutron star, also called a pulsar. It consist of free neutrons, nuclear cores and electrons, plus a few other elementary particles. If the rest after the supernova explosion is greater than 3Msun, no known force can stop the gravitational pull inwards, and we get a singularity, also called a black hole. Supernovae Type 2 Neutron star (pulsar) Black hole Stellar Classification Stellar classification is a classification of stars based on their spectral characteristics. There are 7 main classifications, and each classification has an index from 0-9 indicating where it is between two classifications. Classification Temperature (K) Actual Color O''' ≥ 33,000 blue '''B 10,000–30,000 blue to blue white A''' 7,500–10,000 white '''F 6,000–7,500 yellowish white G''' 5,200–6,000 yellow '''K 3,700–5,200 orange M ≤ 3,700 red